This invention relates to an ink sheet, a recording medium and a recording method for laser thermal transfer recording, particularly relates to an ink sheet, a recording medium and a recording method for laser thermal transfer recording by which peeling for development can be stably carried out within a relatively wide range of the peeling condition.
Recently, a need for direct digital color proof (DDCP) is raised in the field of printing accompanied with widespreading of the image forming technology using digital data. In the DDCP process, high color reproducibility and a stable repeatability are required.
The transferring ability of an ink layer is varied according to peeling conditions, such as a temperature change of the thermal recording medium caused by time passing after the thermal transfer, a peeling speed and a peeling angle, of the thermal transfer recording medium. Therefore, the transfer is made unstable when the peeling condition is unstable.
The influence of the conditions is made larger when the peeling is carried out with a small peeling angle after cooling the thermal transfer medium by leaving for a time after the thermal transfer in a high resolution laser thermal transfer recording process. In such the case, the unevenness of the peeling conditions tends to directly cause a defect such as density unevenness.
Moreover, the transfer at a part exposed to a weak laser light is not easily occurred when the peeling angle is insufficient. Accordingly, such the part is not transferred and a reed screen-like defect in the direction of laser scanning is caused.
For avoiding such the problem, a material is used for improving the peeling ability between the ink layer and the light-heat conversion layer, cf. Japanese Patent Publishing Open to Public Inspection (JP-A) No. 8-267916, and a peeling roller having a relative small diameter is used for fixing the peeling conditions with a large peeling angle as possible.
However, an unevenness of peeling tends to be formed in a high energy recording process using a usual recording material and a usual inter transfer recording medium, since the force necessary for peeling is raised in such the case. On the other hand, some problems are caused such as the apparatus is made complex or an image damage is caused by the transporting with a large curvature, when the peeling roller is used.
The use of the peeling roller having a simple peeling guide is advantageous for reducing the cost and preventing a trouble in the course of transportation. In such the case, it is needed to improve the recording materials so that the peeling development thereof is not dependent on the peeling conditions.
It is found that the peeling development can stably be performed within a relative wide range of the peeling condition by selecting the physical properties of the ink sheet and the inter-transfer medium or image receiving sheet, and this invention is attained.
The object of the invention is to provide an ink sheet, a recording medium and a recording method for laser thermal transfer recording by which peeling for development can be stably carried out within a relative wide range of the peeling condition within a relative broad region.
It has been found that providing a thermoplastic layer and selecting matting agent improve the close contact of the sheets mutually as well as peeling characteristics.
The invention and its embodiments are described below.
A laser thermal transfer recording method of the invention comprises the following steps,
superposing a laser thermal transfer ink sheet having a light-heat conversion layer and an ink layer on a laser thermal transfer image receiving sheet having a thermoplastic layer and an image receiving layer;
contacting with a vacuum a surface of the ink layer of the ink sheet with the surface of the image receiving layer of the image receiving sheet;
thermally transferring a part of the ink layer to the image receiving layer by light-heat conversion of laser light irradiated from the ink layer side; and
peeling off the ink sheet from the image receiving sheet,
wherein Vicat softening point of the resin of the thermoplastic layer is not more than 80xc2x0 C., and one of the image receiving layer and the ink layer contains a matting agent having a particle diameter larger than the thickness of the layer containing matting agent, the projection height of the matting agent is less than 3.5 xcexcm and the frequency of the projections is from 400/mm2 to 4,000/mm2, and peeling angle of the ink sheet and the image receiving sheet is controlled at an angle less than 30xc2x0.
It is preferred that the laser thermal transfer ink sheet and the laser thermal transfer image receiving sheet are superposed on a drum, laser light is irradiated in the condition of superposed state on the drum, and the peeling angle is an angle between tangential direction of the drum and direction of the ink sheet during peeling.
The ink layer preferably comprises a thermoplastic resin having a dry bulb softening point of from 60 to 150xc2x0 C. in an amount of 65% to 95% by weight, and the thickness of the ink layer is preferably 0.3 to 0.7 xcexcm.
The ink layer preferably comprises at least two kinds of thermoplastic resin having a dry bulb softening point of from 60 to 150xc2x0 C. and difference of the softening point of thermoplastic resin having the highest softening point and that of thermoplastic resin having the lowest softening point is from 20xc2x0 to 80xc2x0 C.
A laser thermal transfer recording medium comprises a laser thermal transfer ink sheet having a support, a light-heat conversion layer and an ink layer, an image receiving sheet having a thermoplastic resin layer and an image receiving layer capable of receiving a part of the ink layer, wherein a thermoplastic resin layer comprises a resin having Vicat softening point of not more than 80xc2x0 C., one of the image receiving layer and the ink layer contains a matting agent having a particle diameter larger than the thickness of the layer containing matting agent, the projection height of the matting agent is less than 3.5 xcexcm, and the frequency of the projections is from 400/mm2 to 4,000/mm2.
The laser thermal transfer ink sheet according to the invention comprises at least a light-heat conversion layer and an ink layer is used, in which the ink layer contains a thermoplastic resin having a softening point of from 60 to 150xc2x0 C. in an amount of from 65% to 95% by weight, and has a thickness of 0.3 to 0.7 xcexcm.
In the above-mentioned, it is preferable that the thermoplastic having a dry bulb softening point of from 60 to 150xc2x0 C. is composed of a combination of two or more kinds of thermoplastic resin and the difference of the softening point of the thermoplastic resin having the highest softening point and that of the thermoplastic resin having the lowest softening point is within the range of from 20 to 80xc2x0 C.
The ink layer preferably contains a matting agent having a particle diameter larger than the thickness of the ink layer, the projection height of the matting agent is less than 3.5 xcexcm, and the frequency of the projections is within the range of from 400/mm2 to 4000/mm2.
A medium for laser thermal transfer recording according to the invention preferably comprises an ink sheet for laser thermal transfer comprising a light-heat conversion layer and an ink layer, and an image receiving sheet for laser thermal transfer comprising a thermoplastic resin layer and an image receiving layer capable of receiving the ink layer of the ink sheet, wherein the thermoplastic resin of the thermoplastic resin layer has a Vicat softening point of not more than 80xc2x0 C., and one of the image receiving layer and the ink layer contains a matting agent having a particle diameter larger than the thickness of the layer containing the matting agent, the projection height of the matting agent is less than 3.5 xcexcm and the frequency of the projections is within the range of from 400/mm2 to 4000/mm2.
It is preferably that the ink sheet having an ink layer comprising a thermoplastic resin having a dry bulb softening point of from 60 to 150xc2x0 C. in an amount of 65% to 95% by weight and a layer thickness of from 0.52 g/m2 to 0.90 g/m2 is used and the peeling angle is set at an angle of less than 30xc2x0.
The thermoplastic resin having a dry bulb softening point of from 60 to 150xc2x0 C. composed of two or more kinds of thermoplastic resin and the difference of the softening point of the thermoplastic resin having the highest softening point and that of the thermoplastic resin having the lowest softening point is from 20xc2x0 to 80xc2x0 C.
A laser thermal transfer recording method according to the invention comprises the steps of contacting with a vacuum the surface of ink layer of the laser thermal transfer ink sheet having a light-heat conversion layer and an ink layer with the surface of image receiving layer of a laser thermal transfer image receiving sheet having an image receiving layer capable of receiving the ink of the ink layer; thermally transferring the ink layer to the image receiving layer by light-heat conversion of laser light irradiated from the ink layer side; and peeling off the ink sheet from the image receiving sheet after sufficiently releasing heat to form a thermally transferred image on the image receiving sheet, wherein a recording medium is used, in which the Vicat softening point of the resin composing the thermoplastic layer of the image receiving layer is less than 80xc2x0 C., and one of the image receiving layer and the ink layer contains a matting agent having a particle diameter larger than the thickness of the matting agent containing layer, the projection height of the matting agent is less than 3.5 xcexcm and the frequency of the projections is from 400/mm2 to 4,000/mm2, and the peeling angle of the ink sheet and the image receiving sheet is controlled at an angle less than 30xc2x0 by a device such as a peeling guide and a peeling roller.